Dispersion hardenable Al-Ni-Mn casting alloys for automotive and aerospace structural components

ABSTRACT

An aluminum casting alloy includes at least about 0.5 wt % Ni and 1-3 wt % Mn. It further includes zirconium or scandium for precipitation hardening during T 5  heat treatment.

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present invention is a Continuation-In-Part Application of the allowed U.S. patent application entitled “An Al—Ni—Mn Casting Alloy for Automotive and Aerospace Structural Components”, Ser. No. 10/325,561.

FIELD OF THE INVENTION

[0002] The present invention relates to aluminum casting compositions, particularly to aluminum alloys containing Ni and Mn which have good properties in T5 temper.

BACKGROUND OF THE INVENTION

[0003] The aerospace and automotive industries continually seek components which can be produced from light metal alloys such as aluminum alloys. The Aluminum Association casting alloy 356.0 (“A356.0”) is one such alloy. Alloy A356.0 contains by wt. % 6.5-7.5 Si, 0.12 Fe, 0.10 Cu, 0.05 Mn, 0.30-0.45 Mg, 0.05 Zn, 0.20 Ti, with the balance being aluminum and incidental impurities. It is noted that the recitation by the Aluminum Association of a single value for composition, rather than a range of values, indicates an upper limit to the amount of that element. Thus the alloy A356.0 does not require Fe, Cu, Mn, Zn, nor Ti.

[0004] In order to obtain the desired strength and ductility for such cast aluminum alloys, the alloys generally are thermally treated. The alloy temper is determined by the properties required in the alloy. A T6 temper is generally necessary for alloy A356.0 to maximize the strength and ductility of the cast product. To achieve a T6 temper, the cast product is subjected to a solution heat treatment and quench followed by an artificial aging process. Typical solution heat treatment involves heating the cast product to temperatures in the range of 450°-560° C. so that soluble alloying elements within the cast product diffuse evenly throughout the product in a solid solution.

[0005] Large cast components may require up to 20 hours of solution heat treatment to achieve a uniform concentration of the soluble elements in the solution. Artificial aging, which follows the solution heat treatment, involves heating the component to a temperature in the range of 120° to 200° C. to achieve a controlled fine dispersion of precipitates within the cast alloy.

[0006] The high temperature solution heat treatment needed to obtain a T6 temper is quite expensive and, furthermore, introduces distortions into the cast product. It may, therefore, be necessary for a cast component in T6 temper to be straightened or machined in order to obtain precisely controlled dimensions.

[0007] In recent years, the automotive industry's demand for large aluminum castings for structural components has increased tremendously. These large components include A, B and C posts, engine cradles, door frames, and the like. Due to their size and complexity, it is very difficult, if not impossible, to apply known straightening practices to these castings. As a result, the cost for producing these components using an alloy requiring solution heat treatment and straightening would be very high.

[0008] One non-heat-treatable alloy is taught in U.S. Pat. No. 6,132,531. That alloy was developed for castings requiring high ductility (>15%) and crushability. Such properties are useful in the manufacture of nodes for a vehicular space frame. A major drawback of that alloy is that it contains beryllium which poses a health hazard during production, and greatly complicates the recycling process.

[0009] A T5 temper involves cooling a cast product from an elevated temperature to the lower temperatures used for artificial aging and, thus, requires less energy to produce than a product in the T6 temper, which requires a higher range of temperatures. It will be appreciated that solution heat treatment (T6 temper) is a costly and often a lengthy process step in the production of cast aluminum alloy products. Any attempt to minimize or eliminate solution heat treatment can increase the efficiency and economics of producing cast aluminum alloy products. However, cast products in the T5 temper, generally, lack the strength and toughness of the same products produced in the T6 temper.

[0010] While some work has been performed to develop cast alloy compositions that would obviate the need for solution heat treatment, such alloys have not exhibited the level of strength and toughness of conventional cast alloys such as A356.0 in the T6 temper that calls for high temperature solution heat treatment.

[0011] Accordingly, a need remains for an aluminum casting alloy which displays good castability, low tendency for hot cracking, good strength and toughness in the as-cast condition and which achieves its desired strength by conditioning to a T5 temper without solution heat treatment.

SUMMARY OF THE INVENTION

[0012] In one aspect, the present invention is an aluminum alloy wherein nickel is the most abundant alloying ingredient.

[0013] In another aspect, the present invention is an aluminum casting alloy comprising:

[0014] about 0.5-6 wt % Ni,

[0015] about 1-3 wt % Mn, and

[0016] at least one element for precipitation hardening during artificial ageing.

[0017] In an additional aspect, the present invention is an aluminum alloy casting comprising:

[0018] about 0.5-6 wt % Ni,

[0019] about 1-3 wt % Mn, and

[0020] at least one element for precipitation hardening,

[0021] a microstructure of the casting comprising aluminum dendrites in a matrix comprised of a eutectic of aluminum versus an AINiMn intermetallic compound, and a relatively fine dispersion comprised of the at least one element for precipitation hardening, at least some of the dispersion disposed in the aluminum dendrites.

[0022] In a further aspect, the present invention is a method of making an aluminum alloy casting, the method comprising:

[0023] preparing a molten aluminum alloy comprising 0.5-6 wt. % Ni, 1-3 wt. % Mn, and Zr in a range from about 0.3-1 wt. %;

[0024] heating the molten aluminum alloy to a temperature above the liquidus;

[0025] casting the molten aluminum alloy in a mold; and

[0026] artificially ageing the casting.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a phase diagram showing the liquidus of the aluminum-zirconium system at the aluminum rich side of the diagram;

[0028]FIG. 2 is a composition map of a sample of an AlNiMnZr alloy, according to the present invention, cast from a temperature of 700 C;

[0029]FIG. 3 is a composition map of a sample of the alloy shown in FIG. 2, according to the present invention, cast from a temperature of 750 C;

[0030]FIG. 4 is a composition map of a sample of the alloy shown in FIG. 2, according to the present invention, cast from a temperature of 800 C; and

[0031]FIG. 5 is a plot illustrating the development of hardness during artificial ageing of the present invention for two different temperature regimes.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention includes aluminum casting alloys containing nickel and manganese, with additions of elements that cause a fine grained precipitate during T5 heat treatment. Zirconiumand/or Scandium are particularly contemplated in this capacity. The composition, further, may also include grain refiners such as Titanium.

[0033] When referring to any numerical range of values herein, such ranges are understood to include each and every number and/or fractions between the stated range minimum and maximum. A range of about 0.5-6 wt. % nickel for example, would expressly include all values of about 0.6, 0.7 and 0.8 wt. % nickel all the way up to, and including, 5.7, 5.8 and 5.9 wt. % nickel. The same applies to each other numerical property and/or elemental range set forth herein.

[0034] A typical zirconium level is about 0.3 wt %. Table A provides suitable broad and narrow ranges of the weight percent of the components of the aluminum casting alloy of the present invention. It is noted that Scandium is a particularly costly element, so for many applications, zirconium is preferred. TABLE A Element Broad (wt. %) Narrow (wt. %) Ni 0.5-6   2-5 Mn 1-3 1-3 Sc 0.5 max 0.1-0.3 Zr 1.0 max 0.4-0.6 Ti (B) 0.3 max 0.3 max Fe 0.3 max 0.3 max Si 0.2 max 0.2 max Aluminum, Balance Balance incidental elements and impurities

[0035] Zirconium and/or scandium are included in the alloy of the present invention to maximize the effect of dispersion hardening in the T5 temper so as to achieve mechanical properties that are similar to the T6 temper of casting alloy A356.0. Consequently, production of the casting alloy of the present invention can be made more economical. Furthermore, castings made of the alloy, in T5 temper will exhibit better dimensional control than castings in T6 temper.

[0036] Additions of iron or silicon to a casting aluminum alloy typically result in the formation of various phases (i.e. constituent particles) that can negatively affect the microstructure of the cast product. Iron may enter phases as Al₉FeNi or Al₆FeNi thereby concentrating nickel in these ternary compounds with concomitant reduction in the volume fraction of Al₃Ni and coarsening of the microstructure. Silicon forms intermetallic compounds such as Al₁₅Mn₂Si₃. Such silicon bearing phases can be in equilibrium with Al₃Ni or Al₁₆Mn₃Ni and participate in low temperature eutectic reactions thereby broadening the solidification range and reducing the castability and hot cracking index of the alloy. Accordingly, it is recommended that the levels of iron and silicon in the alloy be controlled to very low levels in order to avoid these effects.

[0037] Although the invention has been described generally above, the following particular examples give additional illustration of the product and process steps typical of the present invention.

EXAMPLES Example 1

[0038] The impact on castability and mechanical properties of nickel levels in as-cast aluminum alloys containing about 2 wt. % manganese was tested. Alloys containing various levels of nickel and a control alloy of A356.0 (T6 temper) were cast into 22 mm diameter ingots. The hot cracking index (HCI) is measure of castability and was measured by a series of pencil probe molds. Mechanical properties of ultimate tensile strength (UTS) and elongation (El) were determined in the as-cast state and after exposure to a corrosive environment, 24 hours in an aqueous solution of NaCl and H₂O₂. The results are reported in Table 1. TABLE 1 Before corrosion After corrosion test test Alloy/ HCI, UTS, UTS, Temper Wt. % Ni mm Mpa E1, % Mpa E1, % 1/F 0 12 98 36 101 — 2/F 0.5 4 121  9 — — 3/F 1 4 146 13 141 16 4/F 2 4 170 — — — 5/F 4 4 201  8 191  7 A356.0/F 0 4 186 — 169  6

[0039] These data shows that a minimum of about 0.5 wt. % Ni is required to achieve good castability (hot cracking index of no more than 4 millimeters). In addition, the overall corrosion resistance was not significantly affected by the total Ni content.

Example 2

[0040] The influence of ancillary additions of various elements on castability (hot cracking index) and mechanical properties of aluminum alloys containing 4 wt. % Ni and 2 wt. % Mn was tested. Table 2 lists the ancillary additions and results of the testing along with data for A356.0 alloy. All the alloys tested exhibited acceptable castability according to hot cracking testing. Titanium addition (Alloy 7) improved elongation over the base alloy (Alloy 6), while Alloy 9 containing scandium addition exhibited significantly increased strength over all alloys following a low temperature heat treatment. The column labeled HB refers to Brinnell Hardness. TABLE 2 Before corrosion After corrosion Wt. %, test test Alloy/ ancillary HCI, UTS, UTS, Temper Element mm Mpa E1, % HB Mpa E1, % 6/F — 4 201 8 59 191 7 7/F 0.1 Ti(B) 4 218 13.3 64 213 11 8/F 0.3 Zr 4 210 6.5 65 194 5 9/T5 0.3 Sc⁽*⁾ 4 283 2.2 100 302 — A356.0/F na 4 186 — — 169 6

Example 3

[0041] Additional alloy compositions set forth in Table 3 were prepared as well as alloy A356.0 in the F temper (as fabricated). Alloys 10, 11, and 13-15 were tested in the F temper, and Alloys 12 and 16 were produced in a T5 temper (3 hour treatment at 300° C.). Testing was performed on 22 mm diameter castings. The mechanical properties, UTS, yield strength (YS) and elongation (El), of the alloys were determined using 6 millimeter samples cut from the castings. Hot cracking index was determined using a pencil probe. The improved elongation exhibited by Alloys 10 and 11 over A356.0, with nearly similar strength properties, is believed to be due in part to the formation of primary crystals of nickel aluminides. Alloy 12 exemplifies the alloy composition of the present invention by including 0.3 wt. % Sc and exhibiting high strength and elongation in the T5 temper. A comparison of Alloy 10 with

[0042] Alloy 13 shows that iron and silicon may be included in the alloy of the present invention without significant impact on the mechanical properties. Alloys 10, 11 and 14 show the as-cast strength is mainly a function of Ni content. Alloys 13 and 15 indicate the ductility decreasing with Fe content when Ni content is 5 wt % but not when the Ni content is 2 wt %. The inclusion of scandium and zirconium was tested in alloy 16 which achieved mechanical properties similar to those of A356.0. TABLE 3 Before corrosion After corrosion test test Alloy Sample UTS, YS, UTS, YS, (Temper) Composition No. Mpa Mpa E1, % Mpa Mpa E1, % AA356.0 7Si—0.3Mg 1 193 98 5.7 184 96 5.0 (F) 2 193 106 5.7 170 112 4.0 3 192 105 6.0 164 103 4.7 4 185 94 6.7 168 98 4.7 Avg. 191 101 6.0 172 102 4.6 10 (F) 2Ni—2Mn— 1 157 82 20.0 148 79 17.0 0.1Ti(B) 2 154 81 20.7 151 84 22.7 3 152 79 24.3 154 83 20.7 4 153 79 20.7 152 84 19.7 Avg. 154 80 21.4 151 83 20.0 11 (F) 4Ni—2Mn— 1 174 103 17.3 170 98 15.0 0.1Ti(B) 2 173 97 18.0 171 95 17.3 3 177 95 15.6 169 91 13.0 4 172 95 15.0 170 101 16.0 Avg. 174 98 16.5 170 96 15.3 12 (T5) 2Ni—2Mn—0.3Sc 1 244 189 11.0 237 186 13.0 2 242 189 11.0 239 188 9.3 Avg. 243 189 11.0 238 187 11.2 13 (F) 2Ni—2Mn— 1 168 81 18.3 159 79 15.3 0.1Ti(B)—0.2Fe— 2 163 81 18.3 159 94 17.7 0.1Si 3 168 84 19.7 153 82 13.3 4 159 81 16.0 155 81 15.7 Avg. 165 82 18.1 157 84 15.5 14 (F) 3Ni—1.7Mn— 1 157 88 20.7 0.1Ti(B) 2 154 84 19.3 3 153 82 15.7 4 158 82 16.0 Avg. 155.5 84 17.9 15 (F) 5Ni—2.2Mn— 1 189 97 4.0 0.1Ti(B)— 2 166 101 4.0 0.2Fe—0.1Si 3 182 111 5.0 4 173 95 3.7 Avg. 177.5 101 4.2 16 (T5) 4Ni—Mn— 1 256 146 6.0 0.1Ti(B)— 2 252 155 5.7 0.3Zr—0.15Sc 3 245 151 5.7 4 239 133 4.7 Avg. 248 146 5.5

Example 4

[0043] Alloys compositions 8 and 9 were also cast in the form of bars machined out of metallic bold castings and having a cross section of 15×30 millimeters. Mechanical properties for these bars appear in Table 4 and indicate that these castings have more dispersed microstructure. In particular, Alloy 9 with the additions of zirconium and scandium in the T5 temper achieves mechanical properties similar to alloy AA356.0 in the T6 temper. TABLE 4 Alloy UTS TYS (Temper) Composition No. MPa MPa E1 % 8 (F) 4Ni—2Mn— 1 199 104 20 0.1Ti(B) 2 200 108 13 3 204 107 16 4 193 100 18 9 (T5) 4Ni—2Mn—0.3Zr— 1 279 198 6 015Sc—0.1Ti(B) 2 280 193 9 3 276 198 8 4 279 198 7

Example 5

[0044] An alloy with zirconium as the only agent for precipitation hardening was cast in the form of bars machined out of metallic mold castings and having a cross section of 15×30 millimeters. The alloy composition had 4 wt % Ni, 2 wt % Mn and 0.5 wt % Zr. Mechanical properties for these bars in T5 temper are shown in Table 5, along with values for A356.0 in T6 temper. This table shows that these castings have properties similar to those of alloy A356.0 in T6 temper. TABLE 5 Alloy TYS, MPa UTS, MPa E % HCI, mm Al—Ni—Mn—Zr 182 270 10 2-4 T5 (avg) A356-T6 210 280 7 2 (Typical)

[0045] Attention is now directed to the figures which provide information relating to the use of zirconium for dispersion hardening during T5 heat treatment.

[0046]FIG. 1 is a portion of the aluminum-zirconium phase diagram 10, showing the vicinity of the liquidus 19 at the extreme aluminum-rich side of the diagram. The abscissa, 11 is zirconium concentration, which, in this figure, ranges from 0 to 1 wt. %. The ordinate 12 is the temperature.

[0047] The region denoted 13 is the liquid. Region 14 is solid aluminum containing a small amount of zirconium dissolved therein. Region 16 is a mixture of the liquid and the intermetallic compound, Al₃Zr. Region 18 is a mixture of solid aluminum and the intermetallic compound Al₃Zr.

[0048] The phase diagram 10 is employed to select a temperature for the molten aluminum alloy prior to casting. The melt temperature should be sufficiently high that the alloy will be above the liquidus of the phase diagram, so that there are no solid phases, notably Al₃Zr, present in the melt. Then, the melt is introduced into a mold and chilled quickly to minimize the time spent in region 16, where Al₃Zr is thermodynamically stable, and in which Al₃Zr tends to precipitate.

[0049] In region 18, Al₃Zr is thermodynamically stable, but because diffusion in the solid is very slow, precipitated particles of Al₃Zr grow very slowly. During artificial ageing, a fine-grained precipitate of Al₃Zr is developed in the aluminum alloy. This fine grained precipitate increases both strength and ductility.

[0050]FIGS. 2, 3 and 4 are composition maps of samples of a cast aluminum alloy containing 2 wt % Ni, 2 wt % Mn and 0.5 wt % Zr. The scale of these figures is indicated by the line segment 30, which has a length of 10 microns. These figures show aluminum dendrites 23 surrounded by eutectic mixture 24. The white areas 26 are particles of Al₃Zr.

[0051] The sample shown in FIG. 2 was cast from a temperature of 700 C, the sample shown in FIG. 3 was cast from a temperature of 750 C, and the sample shown in FIG. 4 was cast from a temperature of 800 C.

[0052] Scaling from FIG. 1 indicates that for an alloy containing 0.5 wt % Zr, the liquidus temperature is about 780 C. Hence, for the sample shown in FIG. 2, which was cast from a temperature of 700 C, the alloy was in region 16 of the phase diagram shown in FIG. 1. As expected, large particles of Al₃Zr are seen in this figure. The large Al₃Zr particles are still present in the sample shown in FIG. 3, which was cast from a temperature of 750 C. However, such large particles of Al₃Zr are absent from the sample shown in FIG. 4, which was cast from a temperature of 800 C.

[0053] A person skilled in the art will recognize that large intermetallic particles generally cause embrittlement, whereas a fine dispersion of intermetallic particles has the potential to increase both strength and toughness. Accordingly, to obtain a casting with good mechanical properties, it should be cast from a melt which is heated above the liquidus for the particular Zr concentration present.

[0054] For an alloy containing 0.5 wt % Zr, a melt temperature of at least about 800 C is recommended. For an alloy containing 0.6 wt % Zr, a melt temperature of at least about 825 C is recommended. For an alloy containing 0.7 wt % Zr, a melt temperature of at least about 850 C is recommended. Likewise, for an alloy containing 0.8 wt % Zr, a melt temperature of at least about 875 C is recommended, for an alloy containing 0.9 wt % Zr, a melt temperature of at least about 900 C is recommended, and for an alloy containing 1 wt % Zr, a melt temperature of at least about 925 C is recommended.

[0055] In order to achieve a fine dispersion of Al₃Zr, artificial ageing is recommended. Two temperature regimes were tested. Schedule 1 consisted of holding the sample at a temperature of 400 C. for 20 hours. Schedule 2 consisted of holding the sample for 3 hours at 330 C, and then at 450 C. for 2 hours. No dimensional changes were seen after these heat treatments.

[0056]FIG. 5 is a plot 40 showing the development of strength during heat treatments according to schedule 1 and schedule 2. The abscissa 42 is time in hours. The ordinate 44 is Brinnell hardness, which is employed as a measure of strength. A number of samples were placed in an oven, and the temperature of the oven was controlled according to either schedule 1 or schedule 2. Individual samples were then withdrawn from the oven at various times. The samples were cooled to room temperature, and Brinnell hardness was measured. Each data point in the figures represents a sample. Curve 46 is for samples treated according to schedule 1 and curve 48 is for samples treated according to schedule 2.

[0057] Regarding the samples treated according to schedule 1 (curve 46), the hardness is seen to increase monotonically until the value of 86 is attained after 20 hours at a temperature of 400 C.

[0058] The samples treated according to schedule 2 (curve 48) developed hardness more quickly than those treated according to schedule 1. For these samples, the maximum hardness, about 88, was attained in about 2 hours at a temperature of 330 C, after which time the hardness stabilized at about 86. Hence, both schedule 1 and schedule 2 resulted in the same value for hardness. Schedule 2 appears to be more economical to implement.

[0059] Alloys of the present invention may be made into shaped castings by high pressure die casting, permanent mold casting, dry sand casting, green sand casting, investment casting and other shaped casting processes.

[0060] While the presently preferred embodiments of the invention have been discussed above, it is to be understood that the invention may be otherwise embodied within the scope of the claims, which follow. 

We claim:
 1. An aluminum alloy wherein Ni is the most abundant alloying ingredient.
 2. An aluminum alloy, according to claim 1, wherein the concentration of Ni is about 4%.
 3. An aluminum alloy, according to claim 1, wherein Mn is the second most abundant alloying ingredient.
 4. An aluminum alloy, according to claim 3, wherein the concentration of Ni is about 4% and the concentration of Mn is about 2%.
 5. An aluminum casting alloy comprising: about 0.5-6 wt % Ni, about 1-3 wt % Mn, and at least one element for precipitation hardening during artificial ageing.
 6. An aluminum casting alloy, according to claim 5, wherein the concentration of Ni is about 2-5 wt %.
 7. An aluminum casting alloy, according to claim 6, wherein the concentration of Ni is about 4 wt %.
 8. An aluminum casting alloy, according to claim 5, wherein the concentration of Mn is about 1.5-2.5 wt %.
 9. An aluminum casting alloy, according to claim 5, wherein the concentration of Mn is about 2 wt %.
 10. An aluminum casting alloy, according to claim 5, wherein the at least one element for precipitation hardening includes Sc.
 11. An aluminum casting alloy, according to claim 10, wherein the concentration of Sc is up to about 0.3 wt %.
 12. An aluminum casting alloy, according to claim 5, wherein the at least one element for precipitation hardening includes Zr.
 13. An aluminum casting alloy, according to claim 12, wherein the concentration of Zr is up to about 1 wt %.
 14. An aluminum casting alloy, according to claim 12, wherein the concentration of Zr is about 0.6%.
 15. An aluminum alloy casting comprising: about 0.5-6 wt % Ni, about 1-3 wt % Mn, and at least one element for precipitation hardening, a microstructure of the casting comprising aluminum dendrites in a matrix comprised of a eutectic of aluminum versus an AlNiMn intermetallic compound, and a relatively fine dispersion comprised of the at least one element for precipitation hardening, at least some of the dispersion disposed in the aluminum dendrites.
 16. An aluminum alloy casting, according to claim 15, wherein the at least one element for precipitation hardening includes Sc.
 17. An aluminum alloy casting, according to claim 16, wherein the concentration of Sc is less than about 1 wt %.
 18. An aluminum alloy casting, according to claim 17, wherein the concentration of Sc is about 0.3 wt %.
 19. An aluminum alloy casting, according to claim 15, wherein the at least one element for precipitation hardening includes Zr.
 20. An aluminum alloy casting, according to claim 19, wherein the concentration of Zr is less than about 1 wt %.
 21. An aluminum alloy casting, according to claim 20, wherein the concentration of Zr is about 0.6 wt %.
 22. An aluminum alloy casting, according to claim 15, wherein the aluminum alloy casting is a structural component of an aerospace product.
 23. An aluminum alloy casting, according to claim 15, wherein the aluminum alloy casting is a structural component of a motor vehicle product.
 24. A method of making an aluminum alloy casting, the method comprising: preparing a molten aluminum alloy comprising 0.5-6 wt % Ni, 1-3 wt % Mn, Zr in a range from about 0.3-1 wt %; heating the molten aluminum alloy to a temperature of at least above the liquidus temperature; casting the molten aluminum alloy in a mold; artificially ageing the casting.
 25. A method, according to claim 24, wherein a concentration of the Zr is about 0.6 wt % and the temperature is at least about 825 C.
 26. A method, according to claim 24, wherein a concentration of the Zr is about 0.7 wt % and the temperature is at least about 850 C.
 27. A method, according to claim 24, wherein a concentration of the Zr is about 0.8 wt % and the temperature is at least about 875 C.
 28. A method, according to claim 24, wherein a concentration of the Zr is about 0.9 wt % and the temperature is at least about 900 C.
 29. A method, according to claim 24, wherein a concentration of the Zr is about 1 wt % and the temperature is at least about 925 C.
 30. A method, according to claim 24, wherein the molten aluminum alloy further includes at least one grain refiner.
 31. A method, according to claim 30, wherein the at least one grain refiner includes Ti, TiB2, and TiC.
 32. A method, according to claim 31, wherein the concentration of Ti is about 0.15 wt %.
 33. A method, according to claim 24, wherein the step of artificially ageing the casting comprises maintaining a temperature of the casting at about 400 C for about 20 hours.
 34. A method, according to claim 24, wherein the step of artificially ageing the casting comprises maintaining a temperature of the casting at about 330 C for about 3 hours and then at about 450 C for about 2 hours.
 35. A method, according to claim 24, wherein the step of casting the alloy is at least one of high pressure die casting, permanent mold casting, dry sand casting, green sand casting, investment casting and other shaped casting processes. 